Paper-like pellicle and method for producing same



Jly'fzz, 195s J. KQHUBBARD' 2,844,491 :PAPER-LIKE PELLICLE AND'rvmiHouFoRv PRonuING SAME .i Filed April 29', i955-A v INVENTOR JAMESK.v HUBBARD 'I L/Qg United States Patent 'O PAPER-LIKE PELLICLE ANDNIETHOD FOR PRODUCING SAME James K. Hubbard, Longview, Wash., assignorto E. I. du Pont de Nemours and Company, Wilmington, Del., a corporationof Delaware Application April 29, 1955, Serial No. 505,040 6 Claims.(Cl. 117-65) This invention relates to a new article of manufacture.More particularly it is concerned with paper and paperlike products fromnylon fibers.

Despite the inherent desirable properties of the wholly synthetic fiberswhich have been commercialized in recent years, these fibers have notbegun to replace cellulose in the manufacture of paper-like structures.The high wet strength, toughness, chemical durability, excellentdimensional stability and ageing qualities of these fibers, should makethem particularly applicable to the field of paper-like products. Onefactor which has hindered the development of the wholly synthetic fibersin this field is the inability of the fibers to fibrillate and bond tothemselves in the manner of beaten cellulose fibers. In addition, inmany cases, commercial papermaking techniques either are not applicableor must be expensively modilied to accommodate the bonding process.

It is an object of this invention to provide a new paper structure fromnylon fibers.

A further object is to provide a nylon paper-like pellicle of high foldendurance.

Another object is to provide a process for the manufacture of nylonfiber paper which is readily adaptable to commercial paper-makingequipment.

These and other objects will become apparent i-n the course of thefollowing specication and claims.

In accordance with the present invention a paper-like pellicle ofanunwoven mass of molecularly oriented synthetic condensation polyamidefibers is bonded with an N-alkoxymethyl polyamide resin. Such materialsare described in Cairns, United States Patent No. 2,467,186. The`bonding of the polyamide fibers is readily accomplished on commercialpaper-making equipment by impregnating an unwoven web or waterleaf ofthe polyamide fibers With an aqueous dispersion of the N-alkoxymethylpolyamide, squeezing to remove the excess liquid, drying the impregnatedweb and thereafter pressing. The resulting product, while exhibiting themechanical and chemical properties of polyamides, possesses foldingendurance values in the order of 700,000 to 1,000,000 cycles and higher.

By an N-alkoxymethyl polyamide resin is meant a polyamide containingrecurring units of the formula:

C o-N- ClHn-O-R wherein R is the non-hydroxyl portion of an alcohol,preferably alkyl or hydrocarbon. Such materials and their aqueousdispersions are described in United States Patent No. 2,467,186.

By a polyamide fiber is meant la funicular structurehaving molecularorientation, such as a fiber, filament, staple and the like producedfrom a synthetic linear polyamide, e. g. as described in United StatesPatent No. 2,071,253 and 2,130,948, by the conventional methods. Amongthe specific polyamides included Within the present invention are thoseformed by the condensation polymerization of a dibasic acid oranamide-forming de- Patented July 22, 1958 ICC Z rivative thereof, suchas adipic, sebacic, suberic, azelaic acids or the like, and a diaminesuch as piperazine, bisamino cyclohexane, ethylene, tertamethylene,pentamethylene, hexamethylene, decamethylene, paraxylylene diamines andthe like. Such materials may also be formed by other well known methodssuch as by polymerization of amino acids or caprolactam.

Figure l is a diagrammatical sketch of a paper-like pellicle produced'inaccordance with the present invention.

Figure 2 is a diagrammatical sketch of an enlarged section of thepaper-like pellicle of Figure l.

In Figure l, the fibrous nature of the pellicle has been emphasized, forin many instances the pellicle has a paper-like finish and the fibersare not apparent.

In Figure 2, the fibers 1 are bonded together by the N-alkoxymethylpolyamide bonding agent 2 of the present invention.

The following examples are cited to illustrate the invention. They arenot intended to limit it in any manner.

All test results to which reference is made in the examples are obtainedby following the procedures reported in TAPPI Standards. Fold endurancetests are made on an M. I. T. Folding Endurance Tester manufactured bythe Tinius Olsen Testing Machine Company).

EXAMPLE I Four grams of 5A; inch, 3 denier per filament staple ofpolyhexamethylene adipamide is suspended in a 6- liter aqueous solutioncontaining 3 grams of sodium carboxymetbyl cellulose. The suspension isdispersed on a Rice-Barton Dyno pulper having two five-inch concavediscs countercurrently stirring at 5000 revolutions per minute atopposite ends of a 5 gallon reservoir. Homogeneity is attained after 2minutes. Thereafter the aqueous dispersion is filtered over an 8" X 8"square of 80 mesh screen, producing a randomly disposed mat of fibersreferred to hereinafter as a waterleaff A vacuum of 350 mm. is employedto facilitate moisture removal and to avert bubble entrainment. Thewaterleaf is gently showered with 2.0 liters of water to wash outresidual sodium carboxymethyl cellulose. The dry waterleaf is thendipped in a 20% solids aqueous dispersion of N-methoxymethylpolyhexamethylene adipamide having 45% of its amide groups substitutedwith methoxymethyl groups. The impregnated sheet is put through squeezerolls to remove the excess dispersion and dried. It is thereafterpressed for 30 seconds at 160 C. under a pressure -of 200 pounds persquare inch. The resulting paper-like pellicle, comprising 89% polyamidebers and 11% by weight `of bonding agent has a tensile strength of 35pounds per inch, a burst strength of 140 pounds per square inch,elongation of 60%, a tearl strength of better than 3200 grams and afolding endurance of 777,329 cycles.

Table l below is a summary of various other fibrous polyhexamethyleneadipamide pellicle preparations illustrating other polymeric dispersionsin comparison with the N-alkoxymethyl polyamide dispersion in variousconcentrations. The fibers, the condition-s and the technique of ExampleI are employed in each example. They average about 2.5 ounces per squareyard.v The impregnated sheets average about 5-8 mils in thickness. HycarAcrylic Rubber #1551 is the trademark of B. F. Goodrich Chemical Co. fora colloidal suspension of an oilresistant butadiene/acryl-onitrilecopolymer rubber in a water emulsion. Chemigum 245AHS is the trademarkof Goodyear Tire and Rubber Co. for a colloidal suspension of an oilresistant butadiene/ acrylonitrile copolymer rubber in a water emulsion.Geon Latex #552 is the trademark of B.l F. Goodrich Chemical Co. for astable water dispersion of a modified polyvinyl chloride resin ofExample-8 isa low softeningplastictypefrnade fromv hexamethylenediamine, adipicacid, sebacic acid and caprolactam to yield a copolymerof approximately 35% or dropped upon a surface, or a continuous lamentmaybe crosslapped-on -a surface; The funicularv-structure may be crimpedor uncrimped and of circular or irregular cross section.

polyhexamethylene adipamideunits;v 38%'epsilon-an1ino- 5 AmongN-alkoxymethyl polyamides which are suitable caproamide units and 27%polyhexamethylene sebacamide in the process of the present invention maybe mentioned units.N Polystyrene Emulsion P VVis an aqueous dis-N-methoxymethylpolyhexamethylenesebacamide,--N-isopersion lofplasticizedpolystyrene-produced by Koppersm'. butoxymethylpolyhexamethyleneadipamide, N-allyloxy- Co- Inc:1 methylpolyhexamethyleneadipamide, the N-benzyloxy- Table I SolidsinF1ber:Binder Tensile Fold En- Exam'yle Binder Dispersion' (Ratio)`Strength durances.:

(percenty (lbs/ln.) (Cycles) Sameas fEx. 1 5 1:0. 2 33 700,000 to1,000,000 SameasEX. 1 10 1:0. 7 47 HfglAcrylie- Rubber 1:0.5 7.9 576ohemium 24-5 Ana.; 5 110.35 1 8.2 l. 1, 638 `PtJlystyyrene Emulsion 51:0. 76 14.3 2, 486 Geo'Latex #552 5 1:0.23 f 26 15,000 'r Copolyamde 51 :0. 34 40 5,

In general the mechanics `of the process described herein methyl1polyamide:4 derivedr-from afmixtureof hexamethyl-A are analogous tothose of paper making. Thus the process 25 ene vdiammoniurn .adipatefandhexamethylen'ediammonium1:v is readily adaptable to paper-.makingequipment, although sebacate, N-furyloxymethylsebacamide,N(betahydroxy):= notlimited thereto. In one embodiment a batt of bers isethoxymethyladipamide, and the like.: formedon a movingscreen. Since theiiberstock can be y. ThefaqueousI dispersion of the N-alkoxymethyl polyft added from a liquid suspension, the Fourdrinier machine; amide`bonding-agentz-is4 appliedto preformed batt in any is convenient forthis operation. The N-alkoxymethyl 30 suitable manner: 'The amount ofbondingresin retainedrf-'r polyamide dispersion, however, should beappliedto the by thebatt Will depend, of course, on the density of the Ybatt `after. its formationon the endless screen. ,Addition batt,;-,;thesolids. concentration of the dispersion and the oftliepolyamidedispersion to the beater or mixer will methodofremoving'the excess dispersion. Vacuum ltrav not produce the outstandingproducts of this invention. tion of the-freshly impregnated batt yieldsthe lowest ratio Adequate heat and pressure for completing the bondingof binder to fiber in the finished product, all other condiof iib'ersissupplied conveniently, by passing the .impreg-v tionsbeingequalgi.Thesimplest method for controlling natedbatt through. heated calenderrolls. Manufacture. porosity of the paper-like productis throughvariation-ofmayalso be performed-on the cylinder paper machineby thesolidstcontent of the aqueous dispersion of N-alkox-y-Similarmodication. methyl polyamide. Binder to liber ratios of less than1-:1A

The method employed in forming the batt is not critical. 40 aregenerally; preferred if a product with any degree of It isfnot necessarythat the molecularly oriented bers be y. porosityfiis desired.y If theproduct contains `as much suspended, in a liquid and beaten prior tobattformation binder as fiber, it is nlm like and hasflow-tearfstrengtlrl since.adherence1among the iibers :does not depend onThebinderato berratiomay be as low as 0.05 :1* and brillation as is thecase in cellulose paper manufacture. provide adequatebonding for many4purposes. lIn general; However, ,to attain uniform distribution it isconvenient. the iratiozwill be between 0.2:1 Aand 0.7:fl for maximum tosuspend .a known weight of fibers or the like in a. v utility.: Toobtain these ratios, theaqueous'dispersionm measured quantity'of liquidand agitate. Machines usedl willfvary Vin solidsc'ontent'between 1 and10%',"Clepending` in paper making'such as the Hollander Beater, the TugfV to some extent'upon the method of removingthe excessboat..Pulper,.-jordans and the like are all suitable. Y Todispersionfromvthe impregnated batt. assist -dispersion the viscosity ofthe liquid may be raised-.50 The bonding step is generally accomplishedAby kex- This fmay. -be accomplished by supplying an additiveto posureof the/resin impregnated batt of nylon'ibersl to v water7 such as sodiumcarboxymethyl cellulose, -partiallyI elevated temperature and pressure.The optimumtem-V hydrolyzed polyvinyl acetate (such as Elvano172-51peratureiwillvary with the speciicN-alkoxymethyl poly.-` manufactured byE. I. du Pont de Nemours and Co. of amidelused, the pressure upon `theba-tt and the period of Wilmington, Delaware), the condensation productof exposure'. For a contact-period'of aboutthirty seconds i ethanolaminewith mixed long chain acids (such as Ninola temperature within the`range of from about Vto 2012A, manufactured by Ninol Laboratories ofChicago, g.- aboutfl70 `-(l. is usuallyf'adequate. While longerhea't-Illinois), or the like, or by employingy a high viscosity'f ingperiods/-When'foperating within this .temperature range liquidsuchasglycerine, ethylene-glycol, t-butyl alcohol may be employed Withoutdeleterious eleets short Peor the like. 'The optimum viscosity will vary,with'the 60 riOds of three minutes-or less are preferred to facilitatetype of mixing or beating, the ber denier, and, similar commercialoperations. lTemperatures suilicient to inducel factors. In choosing thesuspending media'and thickener,l molecular r a-ndornl221tonCause'e-*Weelenlug of the Prodtherefore, care must `be' exercised toavoid substancesz; not and loss of fleXbllltY- .For the Production 0f awhich ;cannot be subsequently removed fromxthe formed; lllghstrengtll,hard Surface PaPerrllle PellCle, e Pressurec batt withfease sincecertain foreign'substances.such'asfor 65 Wltlllnerange 'of from about 50to about 500 Pounds v instance sodium carboxymethylcellulose, even yinminutey L Per 'Squal'elnoll 1's usually employed-"AfA loWer Pressure..concentrations, have been found to interferewith -thex- (0 t0 5 lbSJProduoes a bulkler Product 0f softer Surface. formation of the join.t Inbatt formationfrom a' liquid The Product Vis a tough, leXble, CoherentPaper-likel suspension the use of staple having a lengthbelow about..lPelllolel" lt S useful' in the-making of Peperv money,as 1 inchwith adenief per-1ament within the range of y.70 a nlte'rmedia,:as a non-wovenfabric,.in the manufacture. from about'lo to about 6'is preferred.Howeverthese.v of reinforced Plastic, as body armor@ .Condenser Paper;values mayvary. Fibers of mixed length and denier in high frequencyelectronicV circuits,` printed electrical are suitable.l Fibers as shortas l; inch are satisfactory. circuits, stencils,.,permanent-1edger,..wallpaper.4 and lthe Instead of-laying the batt from liquidsuspension, staple; 1ike..`Whilel the. invention has.l been `exemplied`in the fiber-'or nlamentin wetfor dry condition may be blown 75productionof atstructures. it is obvious :that shaped 5 articles may besimilarly formed by depositing the batt or leaf over a form andthereafter applying the necessary heat and pressure. The seamless cones,bags, apparel and the like may be made.

Many-equivalent modificati-Ons within the inventive concept will beapparent to those skilled in the art from a reading of the foregoingdescription without a departure from the inventive concept.

What is claimed is:

1. A process of preparing a paper-like pellicle which comprisesimpregnating an unwoven web of a molecularly oriented syntheticcondensation polyamide fiber with an aqueous dispersion of anN-alkoxymethylpolyarnide and thereafter subjecting the impregnated massto heat and pressure. y

2. The process of claim 1 wherein the polyamide ber is hexamethyleneadipamide.

3. The process of claim 1 wherein the N-afkoxymethylpolyamide isN-methoxymethyl polyhexamethylene adipamide.

4. A paper-like pellicle comprising an unwoven mass' of a molecularlyoriented synthetic condensation polyamide fiber adhered at points offiber intersection with N-alkoxymethylpolyamide.

5. The product of claim 4 wherein the ber is hexamethylene adipamide.

6. The product of claim 4 wherein the N-alkoxymethylpolyamide isN-methoxymethyl polyhexamethylene adipamide.

References Cited in the le of this patent UNTTED STATES PATENTS2,714,075 Watson et al. July 26, 1955 2,714,097 Watson et al. July 26,1955 2,715,588 Graham et a1 Aug. 16, 1955 2,774,687 Nottebohm et al Dec.18, 1956 OTHER REFERENCES Merriam-Websters New International Dictionary,2nd ed. page 2894, item Web.

1. A PROCESS OF PREPARING A PAPER-LIKE PELLICLE WHICH COMPRISESIMPREGNATING AN UNWOVEN WEB OF A MOLECULARLY ORIENTED SYNTHETICCONDENSATION POLYAMIDE FIBER WITH AN AQUEOUS DISPERSION OF ANN-ALKOXYMETHYLPOLYAMIDE AND THEREAFTER SUBJECTING THE IMPREGNATED MASSTO HEAT AND PRESSURE.